1991 Mercruiser 5.7 closed cooling system with NO sea water pump

[drodkey]

While replacing manifolds and risers on my 1991 5.7 Alpha 1 Gen 2, I stopped in at my mechanic to pick up a new thermostat. While talking he mentions I should take a look at the sea water pump impeller. I reminded him he replaced it last year when I had the stern drive rebuilt. He clarifies the belt driven sea water pump. I start showing him pictures of my engine and he points out that the previous owner who had the closed cooling system installed stopped short of installing the sea water pump, hose and thru haul. We looked through the catalogs and couldn’t find a closed cooling system that ran solely off the stern drive water pump. Basically I have coolant running through the block and manifolds and sea water running through the heat exchanger and risers. Does anyone know of a factory closed cooling system with this set up? Mechanic suggested switching to a 140 thermostat due to the decreased cooling from the lack of sea water volume. Boat is used exclusively in salt water (Puget Sound).

thanks,
Dave

 

[Scott Danforth]

Most aftermarket heat exchanger kits use just the raw water pump in the leg

 

[achris]

1. Ignore that mechanic, he hasn't a clue what he's talking about. (suggest you find another)
2. DO NOT change to a 140 thermostat, use a 160.
3. Yes, closed cooling was offered without an engine driven seawater pump. The only requirement for an engine driven seawater pump with a closed cooling system was if the water temperature was in excess of 84F. Less than that and you can use the drive pump.

Chris........

 

[drodkey]

Most aftermarket heat exchanger kits use just the raw water pump in the leg

With this being a Mercruiser brand would that change anything?

 

[drodkey]

Thanks for the quick replies. I did install the 140, but will order a 160 tonight and swap it out.